IBF Simulation and Progress of Transparency of low Electron to Graphene

Membrane Measurement

Xiao Zhao

Superior：Chengguang Zhu

2017/11/10

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Outline

• Physic Background

• Modified Triple GEM

• Simulation with Modified Triple GEM

• R&D of Measurement Transparency of Electron to Graphene Membrane

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Physics background

p Main Tracking Detector——TPCü Excellent tracking performance, low material budget and structural simplicityü Widely used----ALEPH，DELPHI，STAR，PANDA，ALICE......ü Readout Modules----MWPC(Multi-wire Proportion Chamber)、GEM(Gas Electron Multiplier)

p Ion Feedback ü Creating space charge effectü Degrade TPC count rate capabilityü Reduce the momentum resolution along the drift length

ü Should have to be neutralized

p Ion Feedback depend on

ü GEM geometryü Electric field

ü Gas, pressureü Detector gain,etc.....

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Physics background

p Transverse diffusion of electrons and ionsu Ion drift along the electric field line basically u Transverse diffusion: electron > ionu Electrons and ions can be absorbed by metal layer

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Transverse diffusion of Ar mixtures for different percentages with some measurements of electron

Transverse diffusion of electron and ion in ar/co2 90-10 gas mixture @2KV/cm

Iondiffusion

ediffusion

Modified Triple GEM

p Typical Triple GEMü Outer diameter 70µm; inner diameter 50µmü Kapton 50µm; cooper 5µmü Pitch 140µmü Drift gap :3mm,1~2mm,1~2mm ü Most flow back ions absorbed by bottom metal of upper GEM

p Modified Triple GEMü Stagger middle GEM foil ü GEM1 & GEM2 to absorb flow back ionsü GEM3 plays major role in generating signal

ü Enlargepitchsize(>transversediffusionofion)ü EnlargegapbetweentwoGEMsü ChangeholediameterofGEMlayerü ChangefieldratioofET1 &ET2ü ΔGEM1=300V,ΔGEM2=350V,ΔGEM3=500Vü ED=150V/cm, EI=2KV/cm

p Extra information and conventionsü Gtot: Total number of electrons produced in the simulation

ü IBF :Ion flow back ratio, ions that reach induction area/Gtot

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Simulation with Modified Triple GEM

p IBF of different pitchu Enlarge GEM layer pitch size to absorb flow

back ions from avalanche

u Voltage add on GEMs u 300v 350v 500v

u Hole diameter of both three GEMsu D = 70µm; d = 50µm

u Transfer field u ET1=300V/mm

u ET2=800V/mm

u Magnent field :1Tu Pressure: 760Torru Temperature:293K

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Ionsflowbackratioofenlargepitch RatioofElectronsreachGEM3andprimaryelectron

Simulation with Modified Triple GEM

p IBF of different hole diameter

u Change top and bottom GEM foil hole diameter u Keep middle GEM hole diameter(D = 70µm; d = 50µm) to absorb more flow back ions

from bottom GEM

u Voltage add on GEMs u 300v 350v 500v

u Transfer field u ET1=300V/mm

u ET2=800V/mm

u Magnet field :1Tu Pressure: 760Torru Temperature:293K

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Simulation with Modified Triple GEM

p Transfer Field u Change transfer field ratio ET1 /ET2

u Voltage add on GEMs u 300v 350v 500v

u Inner hole diameter of three GEMsu 70-50-70µm

u Transfer field u ET2=800V/mm

u Magnet field :1Tu Pressure: 760Torru Temperature:293K

p Stagger triple GEM with :p Pitch :300 micron p Top and bottom gem hole diameter:90-70p Middle GEM hole diameter :70-50p Trsfer field ET1=220V/mm ET2=800V/mm

p IBF~ 0.08%（ 13%）with gain ~103

p Disadvantages:p Lower gain p Low resolution 8

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Physics background

p Grapheneü A single layer of carbon atoms(0.335nm)ü Withstand an irradiation up to approximately 1016 ions/cm2 at tens of

keV energiesü Exhibithigh transparency to electrons ranging from tens of keV up to

300 keVü Impermeable to atoms, molecules and ionsü Eliminate the ion back-flow ideally

p New Ideasü Graphene-coated GEMs

ü Graphene as the device to reduce the ion back flow continuously----only allow electrons through graphene layer

ü Stable operation in long time

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single-layer graphene on cooper foil

Transparency Measurement Procedure

pTransparency measurement procedure

ü Measure the leakage current without light. (leakage current should be controlled <10fA)

ü Shift electrode B’ to the foucused electron “beam” center, where the current on collector should be maximum, calculate the current on the SiN holes using beam profile, check the transparency of the SiN holes

ü Shift structure B to the beam, if graphenetransparency is not 0, measure it as the procedure above. If it is 0, no current should be observed.

ü Redo above by adjust the potential ratios between cathode/anode and anode/collector

ü Many questions need to be resolved

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moduleA

moduleB

moduleB'

moduleC

Electron Beam Generation Device

Major Plans & Design

p Problems need to be resolvedü Due to the scattering of electron with gas molecules, the energy

of electron in gas can’t increase much(<10eV)，and hard to adjust

ü Test the transparency of low energy electron through graphene layer in vacuum----to measure the relationship between the transparency and the electron energy precisely

ü How to transfer graphene from cooper to GEM----in our test may be resloved by using SiN grid covered with graphene layer

ü Electron Beam Generation Device----photocathode----MCP(most possible)----more possible options

ü Energy and distribution of electron emitted from mcp ü High Gainü Low Noiseü Large Dynamic Rangeü Emit electron (not known)

Measure the energy & distribution of MCP emit electron (in preparation)

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0.5x0.5mmwindowwithholeysiliconnitridemembraneimagedfrombackside

Measurement Systemp Instruments

ü Light Sourceü MCPü Vacuum Chamber(< 6*10-8b)ü XYZ motor and XYZ controlü Cable：

----XY control----Power supply（3 cables）----Signal cable（tens of cables）

ü Ammeter(Keithley 6482)ü Readout electronics

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Measurement System

pElectron energy & distribution of MCP

ü Measure the leakage current without light. ü Measure the energy and distribution of

emit electrons of MCPü Add voltage between two PCB board and

observe if there's a currentü If not, adjust the position of PCB and voltage

until there's a current ü Redo above to scan electron energyü the anode aignal is read out from PCBü Read data from ammeter

ü Offline analysis

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PCB

Thanks for your attention!

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